Along shorelines of rivers, lakes, bays, estuaries, and ocean coastal shorelines, revetments are used to prevent erosion and loss of property. Many of these locations require aesthetically pleasing revetment structures as part of the evaluation criteria therefore. Traditional schemes of shoreline protection have used quarried stone for this purpose; but stone sources are either becoming depleted or mining of the required stone has become environmentally unattractive in many parts of the U.S. and throughout the world. Also, in many areas, quality stone is very expensive material to use for an erosion control structure. As a less expensive substitute, concrete armor units are frequently used.
Concrete armor units and erosion protection modules are made in a variety of shapes and sizes. Many such structurally complex breakwater armor units are illustrated and briefly described in a flyer entitled "Breakwater Armour Blocks" by the Hydraulics Research Station, Wallingford Oxfordshire, England. Moreover, U.S. Pat. Nos. 2,909,037; 3,176,468; 3,456,446; 3,614,866; 3,636,713; 3,759,043; 4,347,017; 4,594,023; 4,633,639; 5,122,015; 5,190,403; and U.S. Design Pat. Nos. 277,609 and 300,863 further illustrate known complex shaped armor units for shoreline revetments. Significant problems of these known armor units include: i) most are aesthetically unacceptable for certain shoreline areas due to their artificial man-made appearance with no provision for making them appear as natural rock; ii) they are generally more expensive to produce on a per-unit basis due to their irregular shapes and attendant longer multi-step manufacturing requirements; iii) many of these units, which form cooperatively a revetment structure, rely on frictional stability only, without the additional advantage of an interlocking nature between each of the units; iv) many blocks have interlocking in only one direction, but wave loading induces forces both along slope (up & down) and normal to slope (into and out of) so blocks must interlock along all major axes; v) some of the existing units offer very little hydraulic resistance to runup and overtopping and therefore offer little protection to property in the lee of the revetment structure and at transitions between the concrete armor and the underlying shoreline slope; vi) many of these armor units lack porosity in the armor layer producing high pressure differentials across the armor layer which contribute to instability of the armor layer; and vii) some of these complex designed armor units have slender members which are susceptible to structural failure.
An armor unit that teaches of a bar-like structure with interlocking design with a circular cross-section is U.S. Pat. No. 3,375,667 by Hard entitled "Revetment Structure and Units Therefore." This unit is intended for long axis horizontal placement along a shoreline where both frictional and interlocking stabilize the overall revetment structure. However, disadvantages of U.S. Pat. No. 3,375,667 include: i) the Hard unit being described and shown for only horizontal placement along the shore due to its inherent physical design which can easily be destabilized and cause catastrophic failure to a revetment structure, whereas the instant invention herein is preferably placed in a vertical position providing extraordinary stability; the instant invention also is very robust and has a keyed central section that offers additional stabilization of the units in a revetment structure; ii) the Hard unit has an inherent weak central rod structure that is prone to failure with time whereas the instant invention is of a robust monolithic construction; iii) the Hard unit will roll if one of the its units displaces out of position, whereas the instant invention has interlocking keyed sections that prevents roll; iv) the Hard unit has little porosity in an armor layer creating more runup and destabilizing forces; v) the Hard unit has no resistance to destabilization normal to slope, which is crucial due to wave-induced back pressures in this direction; and vi) the Hard unit lacks aesthetics for incorporation in a natural looking revetment structure whereas the instant invention has varied ways to make the end portions of the armor unit congruous with the natural surroundings.